Technical Field
The present disclosure includes antisense oligomers targeted against bacterial genes involved in a biochemical pathway and/or cellular process, and related compositions and methods of using the oligomers and compositions to treat an infected mammalian subject, for example, as primary antimicrobials or as adjunctive therapies with classic antimicrobials.
Description of the Related Art
Currently, there are several types of antibiotic compounds in use against bacterial pathogens and these compounds act through a variety of anti-bacterial mechanisms. For example, beta-lactam antibiotics, such as penicillin and cephalosporin, act to inhibit the final step in peptidoglycan synthesis. Glycopeptide antibiotics, including vancomycin and teichoplanin, inhibit both transglycosylation and transpeptidation of muramyl-pentapeptide, again interfering with peptidoglycan synthesis. Other well-known antibiotics include the quinolones, which inhibit bacterial DNA replication, inhibitors of bacterial RNA polymerase, such as rifampin, and inhibitors of enzymes in the pathway for production of tetrahydrofolate, including the sulfonamides.
Some classes of antibiotics act at the level of protein synthesis. Notable among these are the aminoglycosides, such as kanamycin and gentamicin. This class of compounds targets the bacterial 30S ribosome subunit, preventing the association with the 50S subunit to form functional ribosomes. Tetracyclines, another important class of antibiotics, also target the 30S ribosome subunit, acting by preventing alignment of aminoacylated tRNA's with the corresponding mRNA codon. Macrolides and lincosamides, another class of antibiotics, inhibit bacterial synthesis by binding to the 50S ribosome subunit, and inhibiting peptide elongation or preventing ribosome translocation.
Despite impressive successes in controlling or eliminating bacterial infections by antibiotics, the widespread use of antibiotics both in human medicine and as a feed supplement in poultry and livestock production has led to drug resistance in many pathogenic bacteria. Antibiotic resistance mechanisms can take a variety of forms. One of the major mechanisms of resistance to beta lactams, particularly in Gram-negative bacteria, is the enzyme beta-lactamase, which renders the antibiotic inactive by cleaving the lactam ring. Likewise, resistance to aminoglycosides often involves an enzyme capable of inactivating the antibiotic, in this case by adding a phosphoryl, adenyl, or acetyl group. Active efflux of antibiotics is another way that many bacteria develop resistance. Genes encoding efflux proteins, such as the tetA, tetG, tetL, and tetK genes for tetracycline efflux, have been identified. A bacterial target may develop resistance by altering the target of the drug. For example, the so-called penicillin binding proteins (PBPs) in many beta-lactam resistant bacteria are altered to inhibit the critical antibiotic binding to the target protein. Resistance to tetracycline may involve, in addition to enhanced efflux, the appearance of cytoplasmic proteins capable of competing with ribosomes for binding to the antibiotic. For those antibiotics that act by inhibiting a bacterial enzyme, such as for sulfonamides, point mutations in the target enzyme may confer resistance.
Escherichia coli normally inhabits the large intestine of humans as a commensal organism. However, it can also cause a variety of clinical infections, and is a leading cause of bacteremia. There has been an alarming increase in the number of antibiotic-resistant strains of E. coli isolated from patients with nosocomial and community-acquired bacteremia. It is not uncommon for strains to be resistant to multiple antibiotics.
Acinetobacter baumannii is a ubiquitous organism that has emerged over the years to be a significant cause of hospital-acquired infections. This change in epidemiology is especially concerning given that A. baumannii has become one of the most antibiotic-resistant Gram-negative pathogens that the medical community faces world-wide. The rapid increase in multi-drug resistance in A. baumannii has left few therapeutic choices for the treating physician. Drugs such as colistin are now frequently used, although colistin-resistant strains have appeared. Acinetobacter baumannii can cause a variety of clinical infections, with pneumonia being one of the most frequent.
The appearance of antibiotic resistance in many pathogenic bacteria, including cases involving multi-drug resistance (MDR), raises the fear of a post-antibiotic era in which many bacterial pathogens were simply untreatable by medical intervention. Thus, there is a need for antimicrobial agents that (i) are not subject to the principal types of antibiotic resistance currently hampering antibiotic treatment of bacterial infection, (ii) can be developed rapidly and with some reasonable degree of predictability as to target-bacteria specificity, (iii) are effective at low doses, and (iv) show few side effects.